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back to article LOHAN finally checks into REHAB

We're pleased to announce that today sees the first of our Rocketry Experimental High Altitude Barosimulator (REHAB) experiments, meaning we'll finally find out if solid rocket motors will fire under simulated high-altitude conditions. Click here for a bigger version of the LOHAN graphic After months of head-scratching, faffing …

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Silver badge

Maybe it's too late

But I think you should stick the mirror support into the ground and not in the box. The thing looks a bit wobbly and if the motor firing will generate any vibration you won't see a thing in the mirror - it will just be one fuzzy, blurry smudge on the video.

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Mushroom

Pressure release on firing

If (when) the motor fires, the pressure in the chamber is going to rise very fast. Are you relying on the latex seal to blow when this happens?

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Bronze badge

Re: Pressure release on firing

The perspex lid is just sitting on the seal. When the motor fires the lid will lift off because it is not actually glued on at all. The safety teather ensures that if the lid lifts of at high speed the lid won't go far enough to hurt someone. The mirror is sacrificial: if the lid destroys the mirror no-one cares because by that point they know that the motor can ignite, which is the only question they are trying to answer.

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(Written by Reg staff) Bronze badge

Re: Re: Pressure release on firing

Nicely summarised - thanks.

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Boffin

Pressure gauge

That pressure gauge looks grand. Maybe every SPB project in future should have that kind of smart kind involved. Now where is the Wallace and Grommet icon?

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Silver badge

Shit! Stop! Just thought of something!

That vacuum pump is going to get all the horrible bits of burning metal/whatever in its gizzards without some kind of intermediary box for those exhaust gasses to go into - could be an expensive test!

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Anonymous Coward

Not so

Once vacuum is obtained, the valve is shut. Remember that the lid is only secured by the vacuum in the chamber: once it reaches ambient pressure, the lid pops off and attempts to take the brick into orbit.

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Thumb Down

Re: Not so

Actually not so again, the lid is secured by gravity at ambient pressure, at simulated altitude it is additionally held in place by the surrounding air pressure. If the motor burns long enough to bring the chamber pressure back to ambient and beyond and start to pressurise the chamber the lid will simply rattle in place like a saucepan lid, I doubt the motor will have enough "output" to pressurise the chamber quickly enough to blow the lid off and test the "brick retainment system"!!!

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Anonymous Coward

Looking good, wobbly mirror as noted above aside

best of British, and Spanish, luck

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Bronze badge
Paris Hilton

Have you tried running both pressure gauges side-by-side, to try and answer the question of what was going wrong initially?

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Silver badge
Boffin

Reliability

The manufacturer doesn't know if the motor will ignite *reliably* under those conditions. One successful test-fire won't say much about reliability. It might be a 10% lucky shot.

Methinks you need to fire at least four. Maybe the manufacturer will supply the motors for free if you return the data?

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Bronze badge
Pint

Is there a daft question?

Combustion requires oxygen, exhaust generates carbon monoxide and dioxide aiding oxygen depletion.....Is there enough oxygen in the container to cope with the needs of the motor to fire effectively and fully to complete burn out ..... and take the exhaust?

Hint, stand back when releasing the lid!

I'll have one of these in the mean time

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Silver badge

Re: Is there a daft question?

It's a solid rocket propellant - the oxidiser is already there in the mix, it does not need ambient air for combustion.

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Re: Is there a daft question?

Rocket fuel carries its own oxygen. That's how it is that you can fire rockets in space and they still work! If you think about it for a moment, the amount of ambient oxygen even at a "mere" 25km altitude will be minimal.

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Re: Is there a daft question?

Most model rockets are combined fuel:oxidiser these days I think. Should be able to run in the complete absence of oxygen - I am guessing that the problem will be getting the ignition going without atmospheric pressure to retard the initial exhaust gases a bit.

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Silver badge
Boffin

Sorry to be pedantic, but...

"AVE head honcho John Licence got in touch to offer us the loan of a shiny and expensive suppressed zero gauge, designed to kick in below 50Mbar and with an accuracy of around 1Mbar."

You almost certainly mean mBar, (as in millibar) not MBar (as in megabar), the difference being nine orders of magnitude.

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Facepalm

50 Megabar? Typo alert!

"AVE head honcho John Licence got in touch to offer us the loan of a shiny and expensive suppressed zero gauge, designed to kick in below 50Mbar and with an accuracy of around 1Mbar."

Methinks that's 50mbar and 1mbar respectively, guys. You wouldn't experience 50Mbar unless you went a long way into Jupiter's atmosphere!

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(Written by Reg staff) Bronze badge

Re: 50 Megabar? Typo alert!

You're right - we'll correct that.

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Meh

when I seen the box

My first thought was a schrodinger's cat experiment.

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Re: when I seen the box

The cat may be considered to be both alive and dead while the box is sealed.

Once the rocket motor has fired, I think we can safely assume that the cat is dead, mind.

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Headmaster

Lessons from history

"In tests, we were able to draw an indicated vacuum of 27.5 inches – equivalent to a pressure of 60mmHg, or an altitude of 60,000ft (18,290m)."

Then later....

"With the pump fired up and connected to the REHAB chamber, we managed to draw a vacuum of 20mbar – equivalent to around 76,500ft, or 23,300m - pretty well spot on our target of 15mmHg."

Aaaagh! One minute it's vacuum in "inches", then it's pressure in "mmHg" then it's pressure in mbar. Several times the units appear compared on against the other in the same sentence!

It's a recipe for disaster. Please just work in one set of units to give the project a chance of working? People with bigger pockets than yours (like NASA) have trashed billions of dollars of equipment due to conversion errors. Learn from history.

Looks like the gauge on the latest equipment you've been given works in mbar. Get all the gauges working in mbar, and cross-calibrate them. Think of your goal target-pressures in mbar, and please never mention "inches" or "mmHg" ever again. Give LOHAN a chance to work at least.

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FAIL

Re: Lessons from history

This is not the only units trouble in the article. The pump is calibrated in millibars (mbar) and the article refers TWICE to Mbar (megabars = 1 million bar). A megabar is either the pressure at the center of Jupiter or the purported attribute of a porn star, but it's certainly not a miilibar.

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Silver badge
Boffin

Re: Lessons from history

This is Vulture Central. They work in furlongs per fortnight, Olympic swimming pools, double-decker buses and the size of Wales...

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Bronze badge

Actually it's Vulture East

so I suspect the relevant units are furlongs per fortnight, Olympic swimming pools, donkeys, and the size of Portugal.

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Mushroom

BOOM!

Looking forward to the pics & video of the wreckage. <LOL>

Good luck peeps.

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Re: BOOM!

Actually I doubt anything very exciting is going to happen, I expect the motor will fire no problem and the rocket exhaust will make a mess of that nice shiny lump of perspex they have for a lid. Is it possible for you to stick a couple of sacrificial layers of clear stickyback plastic onto the perspex to prevent damage, that way you'd be able to re-use the perspex/chamber in other SPB projects.

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Trollface

Re: BOOM!

I suspect the shiny lump of perspex will land in France about 45 minutes after the test. And it won't be shiny. It will be a lump - but blackened and twisted. The French government will probably call the Spanish ambassador in "for a chat" and he'll summon the conquistadores to head into the hills, round up the El Reg culprits and "deport" them from the country forthwith!

That's "deport" as in minus their heads. The heads will be left on pikes at the roadside to discourage anyone else trying such a thing!

:-) (In case you hadn't guessed)

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Paris Hilton

Nice view of the hot action.

Mirrored ceiling for the chamber? LOHANs namesake would surely approve.

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Alert

Don't get me wrong, I love a bit of shedgineering, but would it not have been easier, and a more reliable test, to simply send a selection of motors up on a platform beneath a weather balloon, and film the attempted ignition at whichever altitude you desire?

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Pyrotechnics on balloons

I realize that the weather across the pond from us in the colonies has been diametrically opposed to ours; witness

the numerous wildland fires, the worst of which was about 80 km S of my QTH. Due to the possibility of an ignitor control failure, Edge of Space Sciences has laid a severe kabosh on carrying ANY pyrotechnics aboard student payloads. We're at great enough risk at starting a grass fire simply from the heat of a tracking vehicle's catalytic converter! To the point: any balloon flights carrying a rocket motor would be well advised to have predicted trajectories well clear of tinder-dry areas. This option is essentially denied us in eastern Colorado, but not to you.

73 de Mike W5VSI, CTO EOSS

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Silver badge
Thumb Down

Odd choice of test scenarios...

"...We shall see. Our plan is to test the motors first at low pressure, without dropping the temperature. If they won't play ball, we'll address that issue first and then get the dry ice in for the -60°C blast..."

I might have thought of testing both low pressure and dry ice together first.

You will have to do them together eventually, so why not do that first? Then, if all is ok, you don't need to waste a second motor.

The way you're doing it, you will HAVE to use at least two motors.....

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Silver badge

Re: Odd choice of test scenarios...

If you test both conditions at the same time and it fails, you don't know which caused the failure.

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Bronze badge
FAIL

Debugging

fail.

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Silver badge

Bah!

While I applaud the doing of science and can only nod in firm approval of the inclusion of duct tape into your test rig, and I certainly admire the thought that has gone into this test, might it not have been easier to design a simple test bed to be attached to a balloon and attempted the firing for real, letting the laws of physics deal with difficult vacuum engineering? A package of fairly inexpensive instruments could have been devised to monitor the test that could have included multiple redundant SSD cameras.

It would have allowed for some fast and dirty preliminary work and a number of tests at different altitudes could have been done in a very short time. No doubt I am missing some vital point here and I want to make clear I am cheering from the cheap seats. It just seems that the team have started to go all NASA in the approach.

Still, I'm looking forward to video footage of the test firing.

Well done that team.

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Pint

I drink to the health of LVE assistance, I have a Martini in front of me as it is 0030. It has to be a pint, because there isn't a Martini glass icon !

Best of luck !

Chris Cosgrove

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JDC

Fire risk?

Hope you've taken into account the fire risk, that bit of Avila is prone to fires, and it'd be a pity to see the area damaged...

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Pint

Hurrah!

Hurrah for Men in Sheds!

That is all.

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